There have been known gas turbine engines incorporating a bearing accommodated within a bearing chamber defined at an intermediate region between a compressor and a turbine in order to rotatably support a rotor. Typically, the bearing chamber is maintained substantially at an atmospheric pressure. This may cause an unwanted flow of compressed air generated by the compressor through the bearing chamber into the atmosphere. To minimize the compressed air to be wasted, conventionally non-contact labyrinth seals are mounted in the compressed-air channel. The labyrinth seal is economical and highly reliable, however, it has disadvantages, among others, that a considerable amount compressed-air is likely to be leaked therethrough into the atmosphere. To cope with this, it has been developed a non-contact brush seal element with wire bristles, which is described in JP 07-217452 (A).
The brush seal element functions as expected under a certain pressure. This in turn means that, under significantly high pressure circumstances, a multi-stage brush seal made of a plurality of serially arranged brush seal elements should be employed. In actual use environments, however, each brush seal element does not undertake substantially the same pressure and the most-downstream brush seal element is subjected to the highest pressure caused by the pressure difference between the upstream and downstream sides thereof. The reason is that the pressure and density of the compressed air decrease but its volume expands and thereby the rate of volume flow passing by the brushes increases substantially in a stepwise manner, which causes that the most-downstream brush seal element is exposed to the highest pressure.
As a result, the brush seal elements positioned on the downstream side, in particular the most-downstream seal element, are more likely to wear out quickly. Therefore, without a sufficient running-in period, the most-downstream brush seal element becomes nonfunctional in a short period of time and then the nonfunctioning is transmitted sequentially to the upstream brush seal elements, which results in a significant reduction in durability and reliability and also a significant increase of maintenance cost of the entire brush seal mechanism used in, for example, gas turbine engines.